The invention relates to a procedure for the measurement of cardiac output in recording the systolic change of impedance of a tissue by placing at least one initial measuring electrode, within the region of an AC/DC electrical signal, in the skin tissue, and a device for the implementation of the procedure.
The quantity of cardiac output is a measuring indicator for pump performance of the heart. It is an authoritative factor for evaluating whether a human organism (or animal) can assumingly resist suggested physical strain (athletes, pilots, astronauts, racing horses). Apart from other parameters, cardiac output is important during operations, to assess a patient's situation.
The previous impedance procedure for the measurement of cardiac output, especially the procedure according to KUBICEK, is based on the AC/DC change of a tissue area including considerable parts of the thorax, which is caused by heart action. The volume change in capacity vessels caused by the systoles, create a measurable change of tissue impedance (under consideration of the hematocrit, the electrode distances and the volume of thoracic cavity), with which cardiac output can be calculated.
An electrical alternating current of a defined frequency and an amperage Im, flows between two current driving electrodes, which define an AC/DC current path in the tissue. Two measuring electrodes are placed between the two driving electrodes and the voltage U.sub.m =I.sub.m Z is measured. In the equation Z is the impedance between the measuring electrodes, whereas cardiac output is derived from changes of dz/dt, depending on time. For this purpose two circular glued electrodes are placed on the neck and on the caudate thorax and a weak alternating current is applied.